A simple way to incorporate a scalar relativistic treatment is to use
scalar relativistic pseudopotentials which can be generated by
ADPACK. The another way is to use fully relativistic j-dependent
pseudopotentials and to switch off the keyword
'scf.SpinOrbit.Coupling'
as follows:

scf.SpinOrbit.Coupling off # On|Off, default=off

Then, the j-dependent pseudopotentials are automatically averaged
with a weight of j-degeneracy when they are read by OpenMX, which
corresponds to scalar relativistic pseudopotentials.
So, once j-dependent pseudopotentials are generated,
you can utilize the pseudopotentials for both the fully and scalar
relativistic treatments. Thus, we recommend that you make a fully
relativistic j-dependent pseudopotential rather than a scalar
relativistic pseudopotential, when relativistic effects are
taken into account. In fact, the calculation in Fig. 26(a) was performed
using the same pseudopotential as in Fig. 26(b) with 'scf.SpinOrbit.Coupling=off'.